A conventional angular velocity sensor will be described as follows with reference to drawings. FIG. 8 is a plan view of a vibrator used in the conventional angular velocity sensor, FIG. 9 is a B-B cross sectional view of arms shown in FIG. 8, and FIG. 10 is an enlarged cross sectional view of the inside of circle “Q” shown in FIG. 9.
In FIGS. 8 and 9, the conventional angular velocity sensor is provided with vibrator 1 for detecting angular velocity, and an electronic circuit (unillustrated) connected with vibrator 1. Vibrator 1 and the electronic circuit are accommodated in an unillustrated casing.
In FIG. 8, vibrator 1 includes shaft 2 and a pair of arms 3 so as to take the shape of a tuning fork. Arms 3 are each provided with drive electrode units 4 and sensing electrode unit 5, and further with monitor electrode unit 6 extending from a part of each arm 3 that is adjacent to shaft 2 to shaft 2.
Drive electrode units 4 receive driving signals which drive vibrator 1. Monitor electrode units 6 detect the state of driving vibrator 1, and then output detection signals. Sensing electrode units 5 output angular velocity signals generated based on angular velocity given to vibrator 1.
Each drive electrode unit 4, each monitor electrode unit 6 and each sensing electrode unit 5 shown in FIG. 8 is provided with bottom electrode 7 formed on a tuning-fork-shaped substrate, piezoelectric film 8 made of piezoelectric material and formed on bottom electrode 7, and top electrode 9 formed on piezoelectric film 8 as shown in FIG. 9. More specifically, a conductive layer which is to become bottom electrode 7 is formed on a main surface of silicon substrate 10, and piezoelectric film 8 is formed on the conductive layer. Then, another conductive layer which is to become top electrode 9 is formed on piezoelectric film 8. These are processed into prescribed shapes by using a well-known photolithography method.
In an etching process in the manufacturing method using the photolithography method, the conductive layers are processed into the prescribed shapes. In a case of producing fine vibrator 1, dry etching is adopted because it allows a specific part to be exclusively etched with high precision. The reason for this is that wet etching, for example, would cause the conductive layers which are to become bottom and top electrodes 7, 9 and piezoelectric film 8 to be etched by the etching solution more than necessary so as to make it impossible to obtain a pattern with a prescribed shape, thereby deteriorating the electric properties.
Dry etching is a well-known microfabrication process and is used to manufacture various semiconductor devices. The dry etching is also suitable to manufacture vibrator 1 of an angular velocity sensor of the present invention, and is particularly suitable to etch thin conductive layers with high precision.
One conventional technique related to the invention of this application is shown in Japanese Patent Unexamined Publication No. 2002-257549.
With reference to FIG. 8, vibrator 1 used in the conventional angular velocity sensor is provided with drive electrode units 4, monitor electrode units 6 and sensing electrode units 5. In general, the thickness of etching for the formation of the electrode units of the angular velocity sensor is made thicker than the thickness of etching a semiconductor. This makes it necessary to overcome the inconvenience shown in FIG. 10. That is to say, etching debris 11 is left on each etched surface 12 after the etching of the conductive layer corresponding to, e.g. bottom electrode 7.
In actual use conditions where electric field 13 (shown with the arrows) is applied as in FIG. 10, it is necessary to overcome the inconvenience of etching debris 11 causing an electric short circuit between top electrode 9 and bottom electrode 7.